This invention relates to unsaturated polyester compositions which are capable of providing superior surface quality and quickly curable. This invention also relates to sheet molding compounds and bulk molding compounds containing fiber reinforcements.
Fiber-reinforced plastics (FRP) based on unsaturated polyester resins have superior characters not only regarding mechanical strength, heat, water and chemical resistance but also regarding productivity, and are applied extensively to bathtubs, water tank panels and bathroom sinks. Recently, unsaturated polyester sheet molding compounds (SMC) and bulk molding compounds (BMC) are recognized as plastic materials for automotice exterior body panels and are applied not only to main exterior panels such as engine hoods, roofs and trunk lids, but also for other exterior parts such as spoilers, air intakes and rocker panels. The SMC and BMC to be used for automotive exterior panels are particularly required to have superior surface quality and fast curing property. If the curing speed of SMC can be increased even by seconds, for example, this alone can improve productivity significantly. For this reason, there have been several proposals for quick cure catalysts (such as disclosed in U.S. Pat. No. 4,278,558), but surface smoothness of SMC is often lost if its curability is increased. It has been known to use thermoplastic resins such as polymethyl methacrylate, polyvinyl acetate, styrene-butadiene block copolymers and lactone-conjugated diene block copolymers for improving surface smoothness (as disclosed, for example, in Japanese Pat. Publication Tokkai 52-148588 and U.S. Pat. 4,287,313). Although surface smoothness of molded products can be improved by using such low profile additives, it is not sufficient if the curing speed is increased.